Clutch system for a transmission

ABSTRACT

A clutch system for a transmission having a clutch assembly and a brake assembly. The clutch system includes a clutch assembly and a brake assembly coupled to a planetary gear set, engine and two electric motors to reduce transmission complexity, costs, and efficiency losses. The clutch assembly also includes a wear compensation mechanism and a clutch separator mechanism.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application of U.S. Ser. No. 13/188,799, filed Jul.22, 2011.

FIELD

The present disclosure relates to a clutch system for a transmission,and more particularly to a clutch system for a transmission having aclutch assembly and a brake assembly.

BACKGROUND

Some current hybrid transmissions feature two electric motors coupled toan internal combustion engine by dual clutches and include gear setscoupled to the clutches and electric motors. Typical prior arttransmissions arrange the electric motors, clutches and gear sets suchthat the actual torque applied by the electric motors and elsewherewithin the transmission is significantly amplified at the transmissionclutches. This higher torque requires larger, more durable clutches tobe fitted into the transmission, increasing size, weight, and cost.Because typical prior art transmissions amplify the torque applied atthe clutches, larger, more powerful electric motors are needed toprovide enough torque to start an engine coupled to the transmission.Larger motors increase the cost and size of the transmission and createadditional packaging difficulties. Thus, there remains a need forimprovement in hybrid electrically variable transmissions.

Some typical prior art transmissions utilize two clutches coupled to theelectric motors and gears within the transmission. Each clutch typicallyrequires a dedicated bearing, increasing friction losses within thetransmission and increasing costs. Thus, there remains a need forimprovement in hybrid electrically variable transmissions.

In many typical prior art transmissions, a clutch disk is forced underpressure into contact with a friction plate to transfer power from afirst set of components to a second set of components. The appliedpressure is relieved when power is no longer to be transferred. However,the clutch disk and friction plate are still left to gently rub againstone another causing friction losses, vibration, and wear. What isneeded, therefore, is a clutch separator mechanism to prevent contactbetween the clutch disk and friction plate when the clutch assembly isdeactivated. As the clutch disk and friction plate wear in typical priorart transmissions, the distance between the clutch disk and frictionplate increases when in the deactivated state. As a result, greatermovement and time is needed to fully activate the clutch assembly. Insome circumstances, the clutch assembly may not be capable of sufficientmovement to fully activate the clutch. Thus, there remains a need forimprovement in hybrid electrically variable transmissions.

SUMMARY

In one form, the present disclosure provides a hybrid transmissionincluding a clutch assembly, brake assembly, and input planetary gearset. The hybrid transmission also includes a first input shaft coupledto the input planetary gear set, and a second input shaft coupled to thebrake assembly, clutch assembly, and input planetary gear set.

In another form, the present disclosure provides a transmissionincluding a transmission input shaft, brake assembly, clutch assembly,and input planetary gear set. The transmission also includes a firstinput shaft coupled to the input planetary gear set and the transmissioninput shaft, and a second input shaft coupled to the brake assembly, theclutch assembly, and the input planetary gear set. The transmission alsoincludes a first electric motor, first electric motor gear set coupledto the first electric motor, second electric motor, second electricmotor gear set coupled to the second electric motor, output gear set,and output shaft coupled to the output gear set. The clutch assemblyselectively couples the second input shaft to the transmission inputshaft and the brake assembly selectively couples the second input shaftto a transmission housing. The second electric motor gear set is coupledto the input planetary gear set, and the first electric motor gear setand the second electric motor gear set are coupled to the output gearset.

In yet another form, the present disclosure provides a clutch separatormechanism including a first clutch assembly having a first clutch diskand a first friction plate. The clutch separator mechanism also includesa first separator spring and a first pair of snap rings. A first snapring of the first pair of snap rings is disposed between the firstclutch disk and the first friction plate, and a second snap ring of thefirst pair of snap rings is disposed on the opposite side of the firstfriction plate. The first separator spring is disposed between the firstclutch disk and the first snap ring of the first pair of snap rings, andapplies a force to the first clutch disk to move the first clutch diskaway from the first friction plate. The second snap ring of the firstpair of snap rings permits the first clutch disk to move a limited,predefined distance away from the first friction plate.

In yet another form, the present disclosure provides a clutch wearcompensation mechanism including a clutch assembly having a splineshaft, a clutch disk mounted upon the spline shaft, and a frictionplate. The clutch wear compensation mechanism also includes a separatorspring, and a pressed ring. The pressed ring is disposed along an innercircumference of the spline shaft and is configured to be disposed in aradial groove perpendicular to the longitudinal axis of an input shaft.The separator spring is disposed between the clutch disk and thefriction plate and applies a force to the clutch disk to move the clutchdisk away from the friction plate. The pressed ring is movable withrespect to the spline shaft in a first direction but not in a seconddirection.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description, including disclosedembodiments, drawings and claims are merely exemplary in nature intendedfor purposes of illustration only and are not intended to limit thescope of the invention, its application or use. Thus, variations that donot depart from the gist of the invention are intended to be within thescope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an exemplary clutch system for atransmission according to the principles of the present disclosure;

FIG. 2 is a table showing exemplary operating modes of the clutch systemfor the transmission of FIG. 1;

FIG. 3 is a schematic representation of an exemplary clutch separatormechanism and exemplary clutch wear compensation mechanism according tothe principles of the present disclosure; and

FIG. 4 is a schematic representation of another exemplary clutchseparator mechanism according to the principles of the presentdisclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates an example schematic representation of a clutchsystem for a transmission in accordance with a desired embodiment. Anengine 10 is coupled to a transmission input shaft 1. The engine 10 maybe any type of internal combustion engine or any other power sourcedesired. The transmission input shaft 1 is coupled by a damper 6 to afirst clutch assembly 16 and also to a first input shaft 2. The firstclutch assembly 16 selectively couples the transmission input shaft 1 toa second input shaft 3. The second input shaft 3 is coupled to a brakeassembly 17. The brake assembly 17 selectively couples the second inputshaft 3 and, thereby, all components coupled to it to the transmissionhousing 5.

The first input shaft 2 is also coupled to an input ring gear 23 of aninput planetary gear set 20. The second input shaft 3 is also coupled toan input sun gear 21 of the input planetary gear set 20. Input piniongears 22 of the input planetary gear set 20 are rotatably mounted on aninput carrier 24 of the input planetary gear set 20. The input piniongears 22 are continuously meshed with the input sun gear 21 and theinput ring gear 23. The input carrier 24 is coupled to an EMA carrier 34of an EMA planetary gear set 30. EMA pinion gears 32 of the EMAplanetary gear set 30 are rotatably mounted on the EMA carrier 34. TheEMA pinion gears 32 are continuously meshed with an EMA sun gear 31 andEMA ring gear 33 of the EMA planetary gear set 30. The EMA sun gear 31is coupled by a shaft 71 to a first electric motor 11 (“EMA 11”). TheEMA ring gear 33 is coupled by a shaft 74 to a second output driver gear62.

A second electric motor 12 (“EMB 12”) is coupled by a shaft 73 to an EMBdriver gear 41 that is continuously meshed with an EMB driven gear 42.The EMB driven gear 42 is coupled by a shaft 72 to a first output drivergear 61. The first output driver gear 61 and second output driver gear62 are coupled to an output driven gear 63 by a chain 90. In oneembodiment, the chain 90 may be a belt or any other connectingmechanism. In one embodiment, the first output driver gear 61, secondoutput driver gear 62, and output driven gear 63 may be continuouslymeshed.

The output driven gear 63 is coupled by a shaft 75 to an output sun gear51 of an output planetary gear set 50. The output sun gear 51 iscontinuously meshed with output pinion gears 52 of the output planetarygear set 50. The output pinion gears 52 are rotatably mounted on anoutput carrier 54 of the output planetary gear set 50. The output piniongears 52 are also continuously meshed with an output ring gear 53 of theoutput planetary gear set 50. The output ring gear 53 is coupled to thetransmission housing 5. The output carrier 54 is coupled to an outputshaft 4 of the transmission.

In one embodiment, the output shaft 4 may be coupled directly to theoutput driven gear 63 or any desired output gearing arrangement may beutilized. In one embodiment, the second electric motor 12 may be coupleddirectly to the first output driver gear 61 or any desired intermediategearing arrangement may be utilized. Likewise, the gearing arrangementswithin the transmission may be modified as however desired within thetransmission.

FIG. 2 is a table showing exemplary operating modes of the clutch systemfor the transmission of FIG. 1. The clutch system may be operated toprovide the transmission with an underdrive input gear ratio(“underdrive”), a one-to-one input gear ratio (“unity”), or to utilizean input brake (“ground”). “On” indicates that the clutch or brake hasbeen activated, thereby, coupling together all components to which it isattached. “Off” indicates that the clutch or brake has been deactivated,thereby, allowing the components to which it is coupled to rotateindependently of one another. With reference to FIG. 1, when thetransmission is to be operated with an underdrive input gear ratio, thebrake assembly 17 (“Brake”) is activated while the first clutch assembly16 (“C1”) is deactivated. Thus, the second input shaft 3 is coupled tothe transmission housing 5 by the brake assembly 17, preventing theinput sun gear 21 from rotating. Because the first clutch assembly 16 isdeactivated, the first input shaft 2 rotates freely of the second inputshaft 3. The arrangement of the input planetary gear set 20 causes theinput carrier 24 to achieve fewer rotations per minute (RPM) than theinput shaft 1.

When the transmission is to be operated with a one-to-one gear ratio,the first clutch assembly 16 is activated while the brake assembly 17 isdeactivated. Thus, the first input shaft 2 and the second input shaft 3are coupled together by the first clutch assembly 16 and rotate at thesame angular velocity. Because the brake assembly 17 is deactivated, thefirst input shaft 2 and second input shaft 3 are free to rotate. Thearrangement of the input planetary gear set 20 causes the input carrier24 to achieve identical RPM as the input shaft 1.

When the transmission is to be operated as an input brake, the brakeassembly 17 and first clutch assembly 16 are activated. Thus, the secondinput shaft 3 is coupled to the transmission housing 5 by the brakeassembly 17 and the first input shaft 2 is coupled to the second inputshaft 3 by the first clutch assembly 16. Therefore, the first inputshaft 2, second input shaft 3, and input sun gear 21 are all preventedfrom rotating. The vehicle may be driven using EMA 11 and/or EMB 12 toprovide electric powered propulsion. The activation of the brakeassembly 17 and first clutch assembly 16 prevents the loss of propulsiveforce out the transmission input shaft 1 by preventing rotation of thetransmission input shaft 1.

The torque applied to the brake assembly 17 and first clutch assembly 16by EMA 11, EMA 12 and the engine 10 is decreased because the brakeassembly 17 and first clutch assembly 16 are coupled to the sun gear 21of the input planetary gear set 20. The reduced torque enables the useof a smaller brake assembly 17 and smaller first clutch assembly 16,thereby, saving costs, allowing for better packaging of thetransmission, and reducing the mass of the brake and clutch assemblycomponents. In one embodiment, the torque applied to the brake assembly17 and first clutch assembly 16 is approximately half that applied in atypical prior art transmission because the brake assembly 17 and firstclutch assembly 16 are coupled to the sun gear 21 of the input planetarygear set 20, thereby, creating an underdrive ratio between the brakeassembly 17 and first clutch assembly 16, and EMA 11, EMA 12 and theengine 10.

In one embodiment, the default state of the brake assembly 17 isdeactivated and the default state of the first clutch assembly 16 isactivated. Typically, a vehicle already in motion will be operated inthe “unity” drive state of FIG. 2. For example, a vehicle already inmotion travelling around town or travelling on the highway will mostlikely be in the “unity” state of operation. The default state of aclutch does not require any hydraulic pressure to maintain the state.Thus, because the default state of the brake assembly 17 is deactivatedand the default state of the first clutch assembly 16 is activated, nohydraulic pressure is required to operate the transmission in the“unity” mode of operation. As “unity” is likely the most frequent modeof operation, hydraulic pressure for activating the brake assembly 17 orfirst clutch assembly 16 will be reduced. Reducing the necessity forhydraulic pressure improves the efficiency of the transmission. Also,the torque required by the electric motors EMA 11, EMB 12 to start theengine 10 is greatly reduced when the transmission is operated in the“unity” mode compared with the “underdrive” mode. Therefore, setting thedefault mode of the transmission to the “unity” mode requires lessbattery power to start the engine 10 using the electric motors EMA 11,EMB 12, thereby, reducing costs and improving packaging.

FIG. 3 is a schematic representation of an exemplary clutch separatormechanism and exemplary clutch wear compensation mechanism according tothe principles of the present disclosure. A clutch disk 319 is coupledto a spline shaft 381. The spline shaft 381 is non-rotatably mountedupon an input shaft 300. A pressed ring 382 is press fit into an innerdiameter of the spline shaft 381. The pressed ring 382 is pressed fitinto the spline shaft 381 with sufficient force that the pressed ring382 cannot freely move with respect to the spline shaft 381. The inputshaft 300 has a radial groove 390 perpendicular to the longitudinal axisof the input shaft 300. In one embodiment, the groove 390 is around theentire outer radius of the input shaft 300.

A friction plate 315 is mounted upon a bearing 387 mounted upon theinput shaft 300. A separator spring 385 is disposed between the bearing387 and the spline shaft 381. In one embodiment, the separator spring385 may be between the clutch disk 319 and the friction plate 315. Inone embodiment, the separator spring 385 may be between any componentsassociated with the clutch disk 319 and any components associated withthe friction plate 315. The separator spring 385 applies a force to thespline shaft 381 and bearing 387 to keep the clutch disk 319 andfriction plate 315 physically separated. When the clutch assembly ofwhich the clutch disk 319 is a part is activated, the clutch disk 319 ismoved into contact with the friction plate 315 and the force of theseparator spring 385 is overcome. The separator spring 385 issufficiently strong such that when the clutch assembly including theclutch disk 319 is to be deactivated, the separator spring 385 is ofsufficient strength to separate the clutch disk 319 and the frictionplate 315.

The groove 390 of the input shaft includes a first groove surface 391and a second groove surface 392. The pressed ring 382 of the splineshaft 381 is located in the groove 390. In one embodiment, the width ofthe groove 390 along the longitudinal axis of the input shaft 300 isapproximately 0.8 to 1.0 mm wider than the width of the pressed ring382. The pressed ring 382 is forced into contact with the second groovesurface 392 by the separator spring 385 when the clutch assembly isdeactivated. Activation of the clutch mechanism causes the spline shaft381 and clutch disk 319 to move towards the friction plate 315 as theapplication force of the clutch assembly overcomes the force exerted bythe separator spring 385. As the spline shaft 381 moves towards thefriction plate 315, the pressed ring 382 leaves contact with the secondgroove surface 392 and moves towards the friction plate 315synchronously with the spline shaft 381. Eventually, the pressed ring382 will contact the first groove surface 391 and be unable to move anyfurther towards the friction plate 315. However, the spline shaft 381must continue to move towards the friction plate 315 until the frictionplate 315 is in contact with the clutch disk 319. The application forceof the clutch assembly is sufficient such that the application forcecauses the spline shaft 381 to slide with respect to the pressed ring382. The spline shaft 381 continues to slide with respect to the pressedring 382 until the friction plate 315 is in contact with the clutch disk319.

Once the clutch assembly is deactivated, the separator spring 385 forcesthe spline shaft 381 to move away from the friction plate 315, thereby,creating a gap between the friction plate 315 and the clutch disk 319.The pressed ring 382 moves synchronously with the spline shaft 381 awayfrom the friction plate 315. Eventually, as the spline shaft 381 andpressed ring 382 continue to move away from the friction plate 315, thepressed ring 382 will once again contact the second groove surface 392.The force of the separator spring 385 is insufficient to move thepressed ring 382 with respect to the spline shaft 381. Therefore, thespline shaft 381 is unable to move any further away from the frictionplate 315. In this manner, wear of the friction plate 315 and clutchdisk 319 is compensated for by movement of the pressed ring 382 withrespect to the spline shaft 381. In one embodiment, the pressed ring 382may be held in place in a first direction with respect to the splineshaft 381 by detents or other mechanisms. In one embodiment, the pressedring 382 need not be a complete ring around the input shaft 300. In oneembodiment, the pressed ring 382 may simply be a mechanism that actswith respect to detents on the input shaft 300. In one embodiment,movement of the pressed ring 382 with respect to the spline shaft 381 isirreversible.

FIG. 4 is a schematic representation of another exemplary clutchseparator mechanism according to the principles of the presentdisclosure. A first clutch disk 418 is non-rotatably coupled to a firstinput shaft 402 and a second clutch disk 419 is non-rotatably coupled toa second input shaft 403. The first clutch disk 418 is free to movelongitudinally along the first input shaft 402 and the second clutchdisk 419 is free to move longitudinally along the second input shaft403. A first pair of snap rings 481, 482 limits the amount the firstclutch disk 418 may move with respect to the first input shaft 402 and asecond pair of snap rings 483, 484 limits the amount the second clutchdisk 419 may move with respect to the second input shaft 403. A frictionplate 415 is rotatably coupled to the first input shaft 402 between thefirst clutch disk 418 and second clutch disk 419. In one embodiment,there may be several friction plates 415. The friction plate 415 neednot be located between the first clutch disk 418 and second clutch disk419.

A first separator spring 485 is disposed between the first clutch disk418 and the associated snap ring 482 closest to the friction plate 415.The separator spring 485 exerts a force against the first clutch disk418 to push the first clutch disk 418 away from the friction plate 415.The associated snap ring 481 furthest from the friction plate 415 limitsthe distance the first clutch disk 418 may move away from the frictionplate 415. A second separator spring 486 is disposed between the secondclutch disk 419 and the associated snap ring 484 closest to the frictionplate 415. The separator spring 486 exerts a force against the secondclutch disk 419 to push the second clutch disk 419 away from thefriction plate 415. The associated snap ring 483 furthest from thefriction plate 415 limits the distance the second clutch disk 418 maymove away from the friction plate 415. The clutch disk 318, associatedsnap rings 481, 482, and separator spring 485 arrangement may beutilized in any transmission or on any occasion in which a clutch isused. In addition, any number of clutch disk 318, snap ring 483, andassociated separator spring 481, 482 assemblies may be utilized.

The first clutch disk 418 is forced into contact with the associatedsnap ring 481 by the separator spring 485 when the first clutch assemblyis deactivated, thereby, creating a gap between the first clutch disk418 and the friction plate 415. Activation force of the first clutchassembly overcomes the strength of the separator spring 485 and forcesthe first clutch disk 418 to move away from the associated snap ring481, and towards and into contact with the friction plate 415. FIG. 4depicts the first clutch disk 418 in its activated state. Oncedeactivated, the separator spring 485, once again, pushes the firstclutch disk 418 back into contact with the associated snap ring 481,thereby, restoring the gap between the first clutch disk 418 and thefriction plate 415.

The second clutch disk 419 is forced into contact with the associatedsnap ring 483 by the separator spring 486 when the second clutchassembly is deactivated, thereby, creating a gap between the secondclutch disk 419 and the friction plate 415. FIG. 4 depicts the secondclutch disk 419 in its deactivated state. Activation force of the secondclutch assembly overcomes the strength of the separator spring 486 andforces the second clutch disk 419 to move away from the associated snapring 483, and towards and into contact with the friction plate 415. Oncedeactivated, the separator spring 486, once again, pushes the secondclutch disk 419 back into contact with the associated snap ring 483,thereby, restoring the gap between the second clutch disk 419 and thefriction plate 415. The gap between the friction plate 415 and theclutch disks 418, 419 reduces friction losses while the clutches aredeactivated, thereby, increasing the overall efficiency of thetransmission. Reduced clutch friction also extends the life of theclutch assemblies. In addition, in some embodiments, the clutchseparator mechanism may allow for reduced tolerances in manufacturingthe transmission components, thereby, reducing manufacturing costs andcomplexity. For example, in one embodiment, the flatness tolerance forthe clutch disks 418, 419 and friction plate 415 may be reduced becauseof the increased gap between the components when deactivated.

In one embodiment, one clutch assembly may feature a larger diameterclutch disk and friction plate than the other clutches. For example, thefirst clutch assembly 16 may feature a larger diameter clutch disk andfriction plate than the brake assembly 17 or vice versa. In oneembodiment, the default state of the larger diameter clutch isactivated, thereby, locking together the components to which it iscoupled. In one embodiment, the larger diameter clutch may be the clutchthat would be activated for highway cruising. In one embodiment, thelarger diameter clutch may be the clutch that the activation of whichestablishes the lowest overall gear ratio for the transmission (i.e.,the lowest ratio of output shaft 4 RPM to engine 10 RPM). Defaultactivation of the clutch that creates the lowest overall gear ratioeliminates hydraulic pressure losses during typical vehicle cruising.Also, default activation of the largest diameter and lowest gear ratioclutch establishes favorable conditions for engine 10 cranking as thetorque of the electric motors 11, 12 is amplified by the gearing andhydraulic pressure is not required to transmit the torque from theelectric motors 11, 12 to the engine 10. The torque amplification allowsfor a reduction in the size of the batteries needed to power theelectric motors 11, 12, saving costs, space, and weight. Also, becausethe larger diameter clutch is activated during cruising, any defects orinconsistencies in the trueness of the clutch disk or friction platethat might result in rubbing between the clutch disk and friction plateare negated since the clutch assembly is already applied. It ispreferable in one embodiment that, should one clutch disk be untrue andrub the friction plate, the smaller clutch disk do so because of itslower mass and torque capacity, thereby, creating less vibrations andless friction losses.

In one embodiment, axial thrust retainer clips may be used to locate theclutch assemblies instead of dedicated thrust bearings. Eliminatingbearings reduces friction losses within the transmission, thereby,improving transmission efficiency. For example, in one embodiment,because some components of the brake assembly 17 do not rotate, thebrake assembly 17 may be retained with axial thrust retainer clips or bysome means other than bearings. In one embodiment, a brake assemblyfriction plate may not rotate.

What is claimed is:
 1. A clutch separator mechanism comprising: a firstclutch assembly, comprising: a first clutch disk; and a first frictionplate, a first separator spring; and a first pair of snap rings,wherein: a first snap ring of said first pair of snap rings is disposedbetween said first clutch disk and said first friction plate, and asecond snap ring of said first pair of snap rings is disposed on theopposite side of said first friction plate, said first separator springis disposed between said first clutch disk and said first snap ring ofsaid first pair of snap rings, said first separator spring applies aforce to said first clutch disk to move said first clutch disk away fromsaid first friction plate, and said second snap ring of said first pairof snap rings permits said first clutch disk to move a limited,predefined distance away from said first friction plate.
 2. The clutchseparator mechanism of claim 1, further comprising: a second clutchassembly, comprising: a second clutch disk; and a second friction plate,a second separator spring; and a second pair of snap rings, wherein: afirst snap ring of said second pair of snap rings is disposed betweensaid second clutch disk and said second friction plate, and a secondsnap ring of said second pair of snap rings is disposed on the oppositeside of said second friction plate, said second separator spring isdisposed between said second clutch disk and said first snap ring ofsaid second pair of snap rings, said second separator spring applies aforce to said second clutch disk to move said second clutch disk awayfrom said second friction plate, said second snap ring of said secondpair of snap rings permits said second clutch disk to move a limited,predefined distance away from said second friction plate, and said firstfriction plate and said second friction plate are the same.
 3. A clutchwear compensation mechanism comprising: a clutch assembly, comprising: aspline shaft; a clutch disk mounted upon said spline shaft; and afriction plate, a separator spring; and a pressed ring, wherein: saidpressed ring is disposed along an inner circumference of said splineshaft, said pressed ring is configured to be disposed in a radial grooveperpendicular to the longitudinal axis of an input shaft, said separatorspring is disposed between said clutch disk and said friction plate andapplies a force to said clutch disk to move said clutch disk away fromsaid friction plate, said pressed ring is movable with respect to saidspline shaft in a first direction but not in a second direction.
 4. Theclutch wear compensation mechanism of claim 3, wherein the applicationforce of said clutch assembly causes said pressed ring to move withrespect to said spline shaft in a first direction and the force appliedby said separator spring is insufficient to move said pressed ring withrespect to said spline shaft in any direction.
 5. The clutch wearcompensation mechanism of claim 4, wherein the pressed ring isconfigured to be disposed in a radial groove perpendicular to thelongitudinal axis of an input shaft having a width 0.8 to 1.0 mm widerthan the width of the pressed ring.